When oxidizing organic saturated aliphatic aldehydes containing 5 to 9 carbon atoms to the corresponding monocarboxylic acids, the overall objective is to obtain the highest yields and product efficiencies at the highest conversion levels in a single pass, thereby avoiding recycle of significant amounts of unreacted starting materials. Catalysts comprising copper and manganese facilitate this objective, since they result in the production of larger amounts of acid per pass than do manganese catalysts alone. However, a disadvantage often resulting from the use of copper-manganese catalysts in aldehyde oxidation processes, particularly ones in which the reaction product must be distilled to recover the desired product, is plating out of copper in the distillation apparatus. Plating out, of course, leads to undesirable mechanical problems, including erosion of reboilers and pump impellers and rapid pump seal failures.
Copending U.S. application Ser. No. 345,890 filed Feb. 4, 1982, assigned to Celanese Corporation which is a continuation-in-part of application Ser. No. 340,689 filed Jan. 18, 1982, now abandoned, which in turn is a continuation of application Ser. No. 210,992 filed Nov. 28, 1980, now abandoned, which is a continuation of application Ser. No. 065,241 filed Aug. 8, 1979 describes such a process. This process provides commercially attractive high carbon efficiencies of aldehyde to acid at high aldehyde conversions. A single stage or two stage liquid phase reactor system generally gives sufficiently high aldehyde conversions so that recycle of unreacted aldehyde is, in most cases, unnecessary. However, when the reaction mixture is distilled to recover the acid, copper tends to precipitate and plate out on the distillation apparatus.
One means of overcoming this problem is to add oxalic acid per se to precipitate copper and manganese from the reaction mixture as their oxalates, prior to the distillation step. This process is described in U.S. Pat. No. 4,289,708, issued Sept. 15, 1981 to Scott et al and assigned to Celanese Corporation. Copper and manganese can also be separated from the reaction mixture by precipitating them, again as their oxalates, by adding an aqueous oxalic acid solution. In this case, the manganese and copper oxalates precipitate into the aqueous phase, which can be readily separated from the organic acid product by decantation. The acid can then be further purified by distillation. However, aqueous oxalic acid cannot be used satisfactorily to treat mixtures containing valeric acid due to this acid's high solubility in water. This process is described in U.S. Pat. No. 4,246,185, issued Jan. 20, 1980 to Wood, Jr. and assigned to Celanese Corporation.
Japanese Patent No. 52-33614, published Mar. 14, 1977, describes the use of the catalyst combination of copper and manganese in the oxidation of acetaldehyde to acetic acid.
A paper entitled "Metal-ion Catalyzed Oxidation of Acetaldehyde" p. 363-381 written by G. C. Allen and A. Aguilo for the Advances in Chemistry Series 76, published by the American Chemical Society, 1968 in a book entitled Oxidation of Organic Compounds Volume II (Gas-Phase Oxidations, Homogeneous and Heterogeneous Catalysis Applied Oxidations and Synthetic Processes, also describes the use of catalysts comprising copper and manganese, and manganese alone, for the oxidation of acetaldehyde to acetic acid. At page 380, this paper states as follows:
"Acetic acid can also be produced by oxidizing acetyl radicals by copper (II); the copper (I) formed could easily be reoxidized by oxygen."
This reoxidation occurs in the reactor or unit and not in the recovery distillation operation.
U.S. Pat. No. 3,361,806, issued Jan. 2, 1968 to Lidov and assigned to Halcon International, Inc. describes the catalytic oxidation of an oil containing cyclohexane, cyclohexanol and other oxygenated products in the presence of manganese alone and manganese with copper.